feat(shares): preview the approval checklist before submit, fix settlement GL option

The Clerk Dashboard's standalone Share Withdrawal Request form never offered a
GL settlement destination -- it always submitted SAVINGS, silently, while the
Cashier's Transaction Entry screen already let a clerk pick any postable GL
account on its CR row. Added the same "Settlement Destination" choice (Savings
/ GL Account) with a searchable GL selector here too, so both entry points to
the same backend endpoint behave the same way.

Both share-withdrawal confirm dialogs (savings settlement and GL settlement, in
transaction-entry.component.ts) now call the backend's new preview-validate
endpoint before showing the confirm dialog, so a clerk sees the same checklist
a manager will see on approval -- a missing GL mapping, an unverified KYC, an
open AML alert -- before committing to the request, not after a manager has
already spent time reviewing it. A failing check is shown, not blocked: real
hard rules are still enforced server-side at approve(). Guarded with a 5s
timeout and a fallback message so a slow or unavailable check can never leave
the dialog looking stuck.

error-handler.interceptor.ts: a document/signature attachment whose row
survives but whose file is missing from the content store now resolves to a
silent 404 (matching the existing image-fetch handling) instead of surfacing a
raw error. Background GET failures (500/501/503) on calls a component already
recovers from (photo, attachment, notes, standing instructions, ...) now
surface as a corner toast instead of a blocking modal that has to be dismissed
-- a write action's failure (POST/PUT/DELETE) still gets the centred,
must-acknowledge dialog, since that is the one thing the user was waiting on.
Also surfaces the backend's real message on a 500 instead of a hardcoded
generic sentence.

Backend counterpart: ClerkShareWithdrawalRequestApiResource (preview-validate
endpoint, shared buildShareWithdrawalChecks()) and
DocumentReadPlatformServiceImpl (missing-file 404) land separately.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/app/clerk/share-withdrawal-request/share-withdrawal-request.component.html

@@ -129,6 +129,31 @@
           <span>* Date of Meeting</span>
           <input type="date" [(ngModel)]="meetingDate" [disabled]="isReview" />
         </label>
+        <label class="inv-form-field">
+          <span>* Settlement Destination</span>
+          @if (!isReview) {
+            <select [ngModel]="settlementMode" (ngModelChange)="onSettlementModeChange($event)">
+              <option value="SAVINGS">Member's Linked Savings Account</option>
+              <option value="GL">GL Account</option>
+            </select>
+          } @else {
+            <input
+              type="text"
+              [value]="reviewRequest?.settlement_mode === 'GL' ? 'GL Account' : 'Linked Savings Account'"
+              readonly
+            />
+          }
+        </label>
+        @if (!isReview && settlementMode === 'GL') {
+          <label class="inv-form-field">
+            <span>* Settlement GL Account</span>
+            <mifosx-gl-account-selector
+              [inputFormControl]="toGlAccountControl"
+              [glAccountList]="glAccountsData"
+              [required]="true"
+            ></mifosx-gl-account-selector>
+          </label>
+        }
         <label class="inv-form-field">
           <span>* Settlement Payment Type</span>
           @if (!isReview) {
@@ -386,14 +411,25 @@
               <td>Date of Meeting</td>
               <td>{{ meetingDate }}</td>
             </tr>
+            <tr>
+              <td>Settlement Destination</td>
+              <td>{{ settlementMode === 'GL' ? 'GL Account' : 'Linked Savings Account' }}</td>
+            </tr>
+            @if (settlementMode === 'GL') {
+              <tr>
+                <td>Settlement GL Account</td>
+                <td>{{ selectedSettlementGlName }}</td>
+              </tr>
+            } @else {
+              <tr>
+                <td>Linked Savings Account</td>
+                <td>{{ account?.savingsAccountNumber || 'None — settlement will not run automatically' }}</td>
+              </tr>
+            }
             <tr>
               <td>Settlement Payment Type</td>
               <td>{{ settlementPaymentTypeName }}</td>
             </tr>
-            <tr>
-              <td>Linked Savings Account</td>
-              <td>{{ account?.savingsAccountNumber || 'None — settlement will not run automatically' }}</td>
-            </tr>
           </tbody>
         </table>